Address transition detector circuit and method of driving same

Abstract: An address transition detector circuit according to the present invention comprises an input terminal, a one-shot pulse generator circuit having an input electrically connected to the input terminal, a first switching device electrically connected between a first and second nodes and brought into a conducting state in response to a one-shot pulse output from the one-shot pulse generator circuit, a second switching device electrically connected between a ground potential node and the second node and driven in response to a signal input to the input terminal, a plurality of switching devices parallel-connected between the first and second nodes and respectively driven in response to a plurality of address transition one-shot pulse signals, and power source potential supplying means for supplying a power source potential to the first node. Therefore, the address transition detector circuit can prevent malfunctions from occurring even if a change in the input signal and an address transition take place at the same time.

Description: This invention relates to an address transition detector circuit (hereinafter called an "ATD circuit") and a method of driving the ATD circuit. From the EP-A-0 105 757 there is known an address transition detector circuit having the features according to the preamble of claim 1. In particular there is described an asynchronous semi-conductor memory device having an address change detector which generates a pulse of a selected pulse width when a change of address signal is detected. The device further comprises means for holding an internal circuit of the device in a non-operating condition for responding to address signals for the duration of such a pulse. The internal circuit does not operate in response to unwanted address signals generated in the course of a change of address information from an external device generated by noise. It is an object of the invention to improve such a known address transition detector circuit in such a way, that the reliability is increased. This object is solved by a circuit having the features of claim 1 as well as by a method having the features of claim 5. Preferred embodiments are defined in the respective dependent sub-claims. An ATD circuit preferably comprises: an input terminal; a one-shot pulse generator circuit having an input electrically connected to the input terminal; a first switching device electrically connected between a first and second nodes and brought into a conducting state in response to a one-shot pulse output from the one-shot pulse generator circuit; a second switching device electrically connected between a ground potential node and the second node and driven in response to a signal input to the input terminal; a plurality of switching devices electrically parallel-connected between the first and second nodes and respectively driven in response to a plurality of address transition one-shot pulse signals; and power source potential supplying means for supplying a power source potential to the first node. A method of driving an ATD circuit, according to the present invention comprises the following steps: a step for bringing a second switching device electrically connected to a ground potential and a second node into a conducting state in response to a change of an input signal from a first potential level to a second potential level; a step for generating a first one-shot pulse; a step for bringing a first switching device electrically connected to the second node and a first node into a conducting state in response to the first one-shot pulse and setting the potential at the first node to the ground potential during a period in which the first switching device responds to the first one-shot pulse; and a step for bringing at least one switching device electrically connected between the first and second nodes into a conducting state based on at least one second one-shot pulse responsive to an address transition after the change of the input signal from the first potential level to the second potential level and setting the first node to the ground potential during a period in which at least one switching device responds to the second one-shot pulse. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of an ATD circuit showing one embodiment of the present invention ; FIG. 2 is a circuit diagram showing one example of a configuration of a one-shot pulse generator circuit 10 shown in FIG. 1; FIG. 3 is a waveform chart for describing the operation of the one-shot pulse generator circuit 10 shown in FIG. 2; FIG. 4 is a circuit diagram showing one example of a configuration of a load circuit 20 shown in FIG. 1; and FIG. 5 is a waveform chart for describing the operation of the ATD circuit shown in FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is a circuit diagram of an ATD circuit showing one embodiment of the present invention. A description will now be made of a configuration of the ATD circuit. A GT signal is input to an input of a one-shot pulse generator circuit 10. The GT signal is used to inform a row-selection end operation of the one-shot pulse generator circuit 10 during an operation of selecting a special memory cell from memory cells disposed in matrix (row x column) form. The output P1 of the one-shot pulse generator circuit 10 is electrically connected to an input of an inverter 13. The inverter 13 inverts the output (P1) produced from the one-shot pulse generator circuit 10 so as to generate a one-shot pulse P2. An output of the inverter 13 is electrically connected to the gate of an N-type metal oxide semiconductor transistor (hereinafter call an "NMOS") 40. The source of the NMOS 40 is electrically connected to a node N11, whereas the drain of the NMOS 40 is electrically connected to a node N10. Further, the respective drains of the NMOSs 41 0 through 41 n are electrically connected to the node N10. The respective sources of the NMOSs 41 0 through 41 n are electrically connected to the node N11. The respective gates of the NMOSs 41 0 through 41 n are supplied with their corresponding one-shot pulses AT 0 through AT n . When a certain column address is designated or specified out of column addresses A 0 through A n , one of the one-shot pulses AT 0 through AT n , which corresponds to the specified column address, is generated. When the column address A 5 is specified, for example, the one-shot pulse AT 5 is generated. There is a case in which a plurality of column addresses are specified. The drain of an NMOS 42 is electrically connected to the node N11 and the source thereof is electrically connected to a ground potential VSS. Further, the gate of the NMOS 42 is supplied with the GT signal which has been described above. The ATD circuit has a means for supplying a power source to change an output signal ATD in this circuit from an initial state to an H level. This means comprises the power source VCC, the node N10 and the load circuit 20 electrically connected between the power source VCC and the node N10. A current is controlled by the load circuit 20. Further, an input of an inverter 31 is electrically connected to the node N10 and an input of an inverter 32 is electrically connected to an output of the inverter 31. An output of the inverter 32 is electrically connected to an output terminal. The inverters 31 and 32 are used to shape the waveform of a signal output to the node N10. FIG. 2 is a circuit diagram showing one example of a configuration of the one-shot pulse generator circuit 10 shown in FIG. 1. The one-shot pulse generator circuit 10 comprises an odd number of inverters 11 1 through 11 m and a two-input NAND gate 12. The odd number of inverters 11 1 through 11 m are electrically series-connected to an input terminal IN and one of input terminals of the two-input NAND gate 12. The other input terminal of the two-input NAND gate 12 is electrically connected to the input terminal IN. An output of the two-input NAND gate 12 is electrically connected to an output terminal OUT. FIG. 3 is a waveform chart for describing the operation of the one-shot pulse generator circuit 10 shown in FIG. 2. When a GT signal input to the input terminal IN is of an L level, the GT signal is first inverted in turn by each of the odd number of inverters 11 1 through 11 m . Accordingly, the one input terminal of the two-input NAND gate 12 is supplied with an H level. Further, the other input terminal of the two-input NAND gate 12 is supplied with the L level (GT signal). Therefore, a potential of the H level is output to the output terminal OUT. A description will now be made of a case where the GT signal changes from the L level to the H level. The one and other terminals of the two-input NAND gate 12 are respectively supplied with the potentials of the L and H levels depending on variations in the GT signal. Since, however, the one terminal of the two-input NAND gate 12 is electrically connected to the input terminal IN through the odd number of inverters 11 1 through 11 m , a predetermined time interval (t 0 ) is taken until the GT signal having the L level is input to the one terminal of the two-input NAND gate 12. Thus, the one terminal of the two-input NAND gate 12 is still supplied with the potential of the H level during the predetermined period (t 0 ). Therefore, the two input terminals of the two-input NAND gate 12 are respectively supplied with the potentials of the H levels, with the result that an output produced from the two-input NAND gate 12 is brought to the L level. After the elapse of the predetermined period (t 0 ), the potential of the output produced from the two-input NAND gate 12 is brought to the H level. Thus, the one-shot pulse generator circuit 10 generates a one-shot pulse (H→ L→H level) only when the input GT signal changes from the L level to the H level. FIG. 4 is a circuit diagram illustrating one example of a configuration of the load circuit 20 shown in FIG. 1. A resistor 21 whose resistance value is relatively large is used so as to provide a small current flow in the load circuit 20. FIG. 5 is a waveform chart for describing the operation of the ATD circuit shown in FIG. 1. The operation of the ATD circuit shown in FIG. 1 will next be described with reference to FIG. 5. (1) When the GT signal is of the L level, the NMOS 42 is brought into a nonconducting state. Thus, the node N10 is maintained at a potential of an H level irrespective of which column address A i (i: 0 ∼ n) would be specified or selected from the column addresses A 0 through A n , that is, irrespective of a decision made as to which one-shot pulse AT i of the one-shot pulses AT 0 through AT n would be generated and a decision made as to which NMOS 41 i of the NMOSs 41 0 through 41 n would be brought into a conducting state. Accordingly, the output signal ATD is brought to the H level. There is a case where the column address is specified in plural form but, even in this case, the node N10 is maintained at the potential of the H level in the same manner as described above. (2) When the GT signal is of the H level, the NMOS 42 is brought into the conducting state. When a desired column address A i (i: 0 ∼ n) is selected from the column addresses A 0 through A n in this condition, the one shot pulse AT i is generated so that the NMOS 41 i is kept in conduction during a predetermined period (t 1 ). Thus, the node N10 is maintained at a potential of an L level in response to the one-shot pulse AT i during the predetermined period (t 1 ). Therefore, a signal having an L level, i.e., a one-shot pulse ATD is output from the output terminal OUT during the predetermined period (t 1 ). (3) When the GT signal changes from the L level to the H level, the one-shot pulse generator circuit 10 generates a one-shot pulse P1 as described above. This one-shot pulse P1 is inverted by the inverter 13 so as to be produced as a one-shot pulse P2. At this time, the NMOS 40 is kept in conduction during a predetermined period (t 2 ) in response to the one-shot pulse P2. Since the NMOS 42 is in a conducting state at this time, the potential at the node N10 is maintained at the L level during the predetermined period (t 2 ). Thus, a signal having an L level, i.e., a one-shot pulse ATD is generated from the output terminal OUT during the predetermined period (t 2 ). Now, consider the case where a change of the GT signal from the L level to the H level and the designation of the column address take place simultaneously. As described above, the NMOS 40 is kept in conduction during the predetermined period (t 2 ) depending on the change of the GT signal from the L level to the H level. At this time, the NMOS 42 is in the conducting state. On the other hand, the NMOS 41 i corresponding to the specified column address is brought into the conducting state during the predetermined period (t 1 ) substantially simultaneously with the process of keeping the NMOS 42 in conduction, as described above. Thus, even when the change of the GT signal from the L level to the H level and the designation of the column address are substantially simultaneously made, the two NMOSs 40 and 41 i are simply brought into the conducting state. When the column address is specified in plural form, (number of column addresses + 1) NMOSs are simply brought into the conducting state. The ATD circuit can be modified in various ways. The one-shot pulse generator circuit may be constructed of a circuit other than that show in FIG. 2, for example. The resistor 21 of the load circuit 20 shown in FIG. 4 may be made up of a load MOS transistor. Further, the NMOSs shown in FIG. 1 may be replaced with P-type MOS transistors and the power source potential VCC may be replaced with the ground potential VSS.

Claims: An address transition detector circuit comprising: an input terminal, (IN); an input circuit having an input electrically connected to said input terminal (IN); a first switching device (40) electrically connected between a first node (N10) and a second node (N11); a plurality of switching devices (410 to 41n) electrically parallel, connected between the first (N10) and the second node (N11), and a power source potential supplying means (20) for supplying a power source potential (V CC ) to the first node (N10), characterized in that the input circuit is a one-shot pulse generator circuit (10), that the first switching device (40) is brought into a conducting state in response to a one-shot pulse output of said one-shot pulse generator circuit (10), that a second switching device (42) is electrically connected between a ground potential node (V SS ) and the second node (N11) and driven in response to an input signal of the input terminal (IN), and that the plurality of switching devices (410 to 41n) is driven in response to a plurality of address transition one-shot pulse signals. The circuit of claim 1, characterized by a first inverter (31) having an input electrically connected to the first node (N10) and a second inverter (32) electrically connected to an output of the first inverter (31). The circuit of claim 1, characterized in that the one-shot pulse generator circuit (10) has an input terminal (IN), a two-input NAND-gate (12) one input of which NAND-gate is electrically connected to said input terminal, and an off number of inverters (11 1 to 11 n ) electrically series-connected between said input terminal (IN) and the other input of said two-input NAND gate (12). The circuit of claim 1, wherein said power source potential supplying means has a power source potential (V CC ) and a resistor (20), electrically connected to the first node (N10). A method of driving an ATD circuit, comprising the following steps: a step for bringing a second switching device (42) electrically connected to a ground potential mode (V SS ) and a second node (N11) into a conducting state in response to a change of an input signal from a first potential level to a second potential level; a step for generating a first one-shot pulse; a step for bringing a first switching device (40) electrically connected to the second node (N11) and a first node (N10) into a conducting state in response to the first one-shot pulse and setting the potential at the first node (N10) to the ground potential during a period in which said first switching device responds to the first one-shot pulse; and a step for bringing at least one switching device (41 o ...41 n ) electrically connected between the first (N10) and the second (N11) nodes into a conducting state based on at least one second one-shot pulse responsive to an address transition after the change of the input signal from the first potential level to the second potential level and setting the first node to the ground potential during a period in which said at least one switching device (41 o ...41 n ) responds to the second one-shot pulse.

Inventors: HONDA TAKASHI, HONDA, TAKASHI, HONDA, TAKASHI, C/O OKI ELECTRIC IND. CO. LTD.
Applicants: OKI ELECTRIC IND CO LTD, OKI ELECTRIC INDUSTRY CO., LTD.
Application year: 1994
Main classification: G11C8
IPC codes: G11C11, G11C8